Descriptive Characteristics of Tropopause on the Atmosphere of Iran in Transitional seasons

Document Type : Full length article


1 Professor in Climatology , Department of Geography, University of Zanjan

2 null

3 Phd Candidate of Climatology (Climate Change), University of Zanjan, Zanjan, Iran.


Extended Abstract
Monitoring the tropopause features over a geographic area is important for a number of interrelated reasons. From a climatological point of view, it is important to investigate the behaviour of the tropopause charactreristics for a long term, so that to detect any increased or decreased trends. From a dynamic point of view, it is essential to define the tropopause hieght, in order to explore the stratosphere—troposphere exchange taking place over a geographic area that may be responsible for changes in the chemical composition of the atmosphere. Over the past two decades, there has been growing interest in the tropopause charactreristics among the atmospheric scientific community. It is now broadly accepted that the tropopause plays a key role in a variety of atmospheric and climatic phenomena.
Materials and methods
Compared to studies performed globally, in Iran a limited number of studies concerning the tropopause have been conducted. Moreover, the methods have been used and the length of the dataset were often inadequate. Therefore, in the present study, for the detection of tropopause, the daily data of Temperature, and Geopotential Height from the European Centre for Medium-Range Weather Forecasts (ECMWF) for 700 to 50 hpa with a spatial resolution of 0.25 × 0.25 longitude/latitude from 1979 to 2018 was adopted. Accordingly, 2491 cells have been covered across Iran. The LRT was used to detect tropopause. the tropopause is defined as ‘‘the lowest level at which the lapse-rate decreases to 2 /km or less, provided that the average lapse-rate between this level and all higher levels within 2 km does not exceed 2C/km. In this study, in addition to the tropopause pressure level, the tropopause height (m) was also evaluated during this period.To obtain better cognitive knowledge about tropopause, the factors that were likely to be related to the spatial changes in height of tropopause were investigated. To achieve this goal, the relationship between tropopause pressure and spatial variables (e.g. longitude, latitude, and elevation) was assessed by general and partial linear correlation ceofeicents. In addition to the characteristics of temperature at the lower and upper levels of the tropopause, the difference in temperature between these two levels on the atmosphere of Iran and the characteristics of the minimum, maximum, average, as well as the temperature range of the earth's surface were evaluated and their relationship with tropopause pressure levels and height levels was assessed.
Results and discussion
Investigating the characteristics of tropopause on the atmosphere of the studied area in the under investigation period (1979 to 2018) and its related factors in the autumn and spring months showed that in the months of these two seasons, various factors affecting height and pressure levels of tropopause are diffrnt and in both seasons have different characteristics. In all spring and autumn except for September, the height of the tropopause is decreasing as the latitude increases, but in October and November, the rate of change was greater than in the other months. In all the months of these two seasons (except September), the highest level of the tropopause taking place in the south-east of the country, whilst the lowest level of pressure occured in the north-west of the country. Investigating the changes in tropopause height and tropopause pressure levels also showed that they were not consistent in the under investigation seasons, so that in places with similar pressure levels, observed elevations were different. the tropopause pressure levels have a strong relation with the latitude, but changes in the tropopause height did not show a regular relationship with latitude.Tropopause height changes are mostly irregular in spring and autumn, and in parts of the country, it is almost dependent on longitude. In the spring and autumn periods, the high and low tropopause levels are among the most influential factors on tropopause. Among the cases that were related to the tropopause were surface temperatures and their characteristics in the spring and autumn seasons. During these two seasons, it was found that the potantial relationship of surface temperatures with tropopause pressure and elevation levels, especially at high latitudes, is low, but in lower latitudes, due to limited variation in the surface temperature, the potantial connection of tropopause and surface temperatures are higher than other parts of the country. In the months of the spring and October and November, it was revealed that the potantial correlation between tropopause pressure and elevation levels with local factors was low, but in September in parts of the country, the effects of surface elevations on the levels of tropopause pressure is much more significent.
The results of the study of the tropopause and its related factors showed that the trend of tropopause pressure changes in the vicinity of latitude is decreasing with increasing the latitude. But the tropopause height is not aligned with its pressure levels, and in most areas, it is in the vicinity of Longitude. Among the studied factors, the low and high levels of tropopause have the highest impact on the tropopause, and the effects of surface temperature and other examined cases have not a noticable impact.
he results of the study of the tropopause and its related factors showed that the trend of tropopause pressure changes in the vicinity of latitude is decreasing with increasing the latitude. But the tropopause height is not aligned with its pressure levels, and in most areas, it is in the vicinity of Longitude. Among the studied factors, the low and high levels of tropopause have the highest impact on the tropopause, and the effects of surface temperature and other examined cases have not a noticable impact.
he results of the study of the tropopause and its related factors showed that the trend of tropopause pressure changes in the vicinity of latitude is decreasing with increasing the latitude. But the tropopause height is not aligned with its pressure levels, and in most areas, it is in the vicinity of Longitude. Among the studied factors, the low and high levels of tropopause have the highest impact on the tropopause, and the effects of surface temperature and other examined cases have not a noticable impact.


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